1. Field of the Invention
The present invention relates to magnetic sensors, and, more particularly, to a dual Hall effect sensor operable with a single magnet to produce two independent outputs each of which changes when an associated magnetic shunting material passes in proximity thereto.
2. Description of the Prior Art
Magnetic sensors which produce outputs when in the proximity of a magnetic field are well known in the art. One variety of such sensor is known as the Hall effect sensor which produces an electrical output indicative of the magnitude of the magnetic field in which it is located. Hall effect sensors have been used in the prior art to detect motion of a ferrous member or other field shunting material which passes close thereto and affects the distribution of the magnetic field of the magnet. One such use for such apparatus is found in automotive applications for distributorless ignition systems. For example, in the Armstrong U.S. Pat. No. 4,222,263 issued Sept. 16, 1980, a crankshaft positioned transducing system is shown having a pair of reference elements mounted circumferentially and at radially spaced locations on the fly wheel with a transducer head having two individual transducers which cooperate with a respective one of the reference elements to produce a trigger impulse. Similar systems are shown in the Kiess et al U.S. Pat. Nos. 4,406,272 and 4,508,092 issued Sept. 27, 1983 and Apr. 2, 1985, respectively. There is, however, a need for a magnetic sensor which can operate to produce two different signals each of which is indicative of the motion of a magnetic field shunting material as, for example again, in automotive applications where it is desired to not only provide distributorless ignition operation but also, for example, to provide other control functions such as the activation of a fuel injection system or an RPM indicator. In the Nichols et al U.S. Pat. No. 4,373,486, which issued Feb. 15, 1983, a dual output sensor is shown wherein a ferrous disk is rotatably driven by an internal combustion engine shaft and upon which there are inner and outer circumferential rims projecting outwardly from one side thereof. Each of the rims has arcuate notches therein and two magnetic sensors are positioned, one to the inside of the inner rim and one to the outside of the outer rim, with a permanent magnet positioned between the two rims. Accordingly, as the disk rotates, the rims move between the magnet and each of the sensors so that the notches cause a disturbance in the magnetic field between the permanent magnet and each of the magnetic sensors. The system thefore produces two outputs utilizing the same permanent magnet.
The difficulty with the Nichols et al system is that it requires that there be two magnetic field shunting material members each of which passes between the permanent magnet and one of the sensors. The motion of a member between the magnet and the sensor is referred to as a "vane" operated system, and it is difficult to provide two "vane" projections for use with the permanent magnet. Extra space in automotive applications is quite scarce and providing two vanes driven by the crankshaft takes up room. Finding space for the sensor is therefor impossible in some situations. Furthermore, the vanes have to be very accurately positioned to rotate between the magnet and the sensors.
Another type of sensor referred to as a "gear tooth" operated system, is known in the art. In a "gear tooth" system, a magnetic sensor is located closely adjacent to one end of a magnet and any available magnetic field shunting material, such as an already existing gear tooth in an automotive system, passes on the other side of the magnetic sensor and not between the sensor and the magnet. Such a "gear tooth" was described at a "technical exchange seminar" presented by Honeywell Microswitch Division on Feb. 4-5, 1986. The "gear tooth" operation is more convenient for use with a magnetic field sensor since already existing equipment can be used as the shunting material and the accuracy problems are alleviated since there is no requirement that a magnetic field shunting material pass between the sensor and the magnet. Accordingly, mounting locations adjacent the rotating parts of the internal combustion engine are more easily obtained than is the case with "vane" operation and with less accuracy difficulties. On the other hand, the output obtained from a "gear tooth" system is somewhat smaller than that obtained from a "vane" system, and the output from the "gear tooth" system may not be of sufficient magnitude for operation of a distributorless ignition system although it may be sufficient for operation of other portions of the automotive system such as the fuel injection system.
Accordingly, it has been desired to provide a magnetic sensing system which can produce two independent outputs yet has some of the advantages of the "gear tooth" system for ease in location, and some of the advantages of the "vane" operation to produce a sufficient output for driving the distributorless ignition system.